CORROSION BEHAVIOR OF NI-CR-BASE COMMERCIAL ALLOYS IN FLOWING AR-42.6-PERCENT-O-2-14.7-PERCENT-BR-2 GAS-MIXTURE ET 700-DEGREES-C

Corrosion behavior of Ni-Cr-Base commercial alloys has been investigat ed in an argon-42.6% oxygen-14.7% bromine Eas mix ture at 700 degrees C which was one of the environments encountered in the UT-3 thermochem ical water decomposition reaction process to produce hydrogen. The tes t alloys were Inconel 600, Hastelloy C-276, Inconel 625, and Nimonic 8 OA. Two-dimensional thermodynamic phase stability diagrams were constr ucted for nickel, chromium, iron, tungsten, cobalt, titanium, and alum inium to predict the condensed corrosion products that are stable with respect to the representative alleging elements when the alloy is exp osed to the argon-42.6% oxygen-14.7% bromine gas mixture at 700 degree s C. The oxides were thermodynamically stable phases with respect to t he corresponding metals. Post-reaction treatment of test alloys includ ed discontinuous mass-change measurements, scanning electron microscop y (SEM), electron probe micro-analysis (EPMA) for morphological and co mpositional investigation of the corrosion products, and the X-ray dif fraction (XRD) for phase identification. XRD identified oxides and spi nels as corrosion products bur low-melting metal bromides were also de tected for all alloys with deleterious effects on high-temperature pro perties of these alloys during exposure to the environment. The poor c orrosion resistance of Inconel 600 and Hastelloy C-276 was mainly caus ed by the cracking and spalling of iron and nickel-rich oxides and fur ther growth of various metal bromides beneath the oxide scale followin g prolonged exposure. Inconel 625 and Nimonic 80A alloys performed bet ter than Inconel 600 and Hastelloy C-276, mainly because of their alum inium alloying element and lower iron content.